Method

Melt the butter, flour and mustard together in a saucepan and cook for 1 minute, stirring, occasionally. Remove the pan from the heat and gradually blend in the milk. Return to the heat and bring to the boil, stirring constantly, until smooth.

Stir in the cheese and pepper and simmer for 1 minute. Remove from the heat and leave to cool slightly. Beat in egg yolks.

Place the egg whites in the bowl, fit the whisk and whisk on speed max for 2-3 minutes, until stiff. Fold 30ml (2tbsp) of the egg whites into the cheese mixture until well blended. Fold in the remaining until well combined. Pour into prepared dishes, sprinkle over remaining parmesan and bake for about 12-15 minutes, until well risen and golden. Serve immediately.